1. Field of the Invention
The present invention relates to an image forming apparatus such as a laser printer.
2. Description of Related Art
Laser printers and other image forming apparatuses mainly include: a photosensitive drum, a developing roller, a transfer roller; and a sheet conveying mechanism. The photosensitive drum is formed with an electrostatic latent image on its outer peripheral surface. The developing roller is disposed in confrontation with the photosensitive drum. The developing roller supplies developing agent, such as toner, to the photosensitive drum, thereby developing the electrostatic latent image into a visible image. The transfer roller is disposed at a transfer position in confrontation with the photosensitive drum. The transfer roller is applied with a transfer bias voltage with a polarity opposite to that of the photosensitive drum. The sheet conveying mechanism conveys a sheet of paper along a sheet transport path in a paper conveying direction toward the transfer position. When the sheet of paper reaches the transfer position, the sheet of paper is brought into contact with the surface of the photosensitive drum.
Especially in non-contact type printers, a charger uniformly charges the outer peripheral surface of the photosensitive drum. A laser generating unit modulates a laser beam based on image data, and scans the laser beam across the outer peripheral surface of the photosensitive drum. As a result, a corresponding electrostatic latent image is formed on the surface of the photosensitive drum. The developing roller conveys, on its surface, toner that is electrically charged to the same polarity as that of the photosensitive drum. The electrostatic latent image on the photosensitive drum is developed into a visible toner image with the toner supplied from the developer roller according to a well-known reversal development process. The thus developed visible image is then transferred, at the transfer position, from the photosensitive drum onto a sheet of paper that reaches the transfer position. The visible image is pulled onto the sheet of paper by an electrostatic field that is generated by the transfer bias applied to the transfer roller. Thus, one image forming cycle is completed.
According to the above-described image forming cycle, some toner remains on the surface of the photosensitive drum after the toner image has been transferred from the photosensitive drum onto the sheet of paper. According to a well-known cleanerless method, this residual toner is collected during the next image forming cycle. Thus, in each image forming cycle, development and cleaning are performed simultaneously by the developing roller according to reversal development process.
According to this cleanerless method, there is no need to provide a blade or the type of cleaner device in the image forming apparatus. There is also no need to provide a vessel to accumulate waste toner. Accordingly, configuration of the entire image forming apparatus can be simplified and made more compact. The image forming apparatus can be produced less expensively.
It is noted that when the sheet of paper reaches the transfer position, the sheet of paper contacts the surface of the photosensitive drum, and paper dust clings to the surface of the photosensitive drum. This paper dust will be possibly collected together with the residual toner. When the toner is reused during a later development process, the paper dust can degrade the resultant visible image. When an acid type sheet is used as the sheet of paper, the paper dust includes filler material such as talc. The filler material can cause filming and so magnify the problem of the defective visible images.
There have been proposed several types of paper-dust removing device such as: (1) a rotational brush roller; (2) another rotational brush roller whose constituent brush fibers are formed in loops; and (3) a rotational non-woven fabric roller that includes a rubber roller covered with a non-woven fabric. The rotational brush roller (2) is disclosed in Japanese patent application publication (kokai) No.HEI-1-11667), and the rotational non-woven fabric roller (3) is disclosed in Japanese utility model application publication (kokai) No.SHO-62-181973.
However, these devices (1) through (3) have the following problems.
Devices (1) and (2) are able to properly remove fibers included in the paper dust. However, the brush in these devices is unable to sufficiently remove filler material such as talc in the paper dust from an acidic paper. As a result, talc will possibly be collected together with residual toner on the developing roller. The collected talc will generate an undesirable fogging phenomenon during subsequent development processes. That is, when an electrostatic latent image is developed with toner mixed with talc, fogging will be formed on the white areas of a developed image and as a result the image will be poor.
Device (3) is designed to strongly press the non-woven fabric against the photosensitive drum in order to properly remove both the fiber material and the filler material from the surface of the photosensitive drum. However, the non-woven fabric will scrape the paper dust across the surface of the photosensitive drum. As a result, the soft talc is spread across the surface of the photosensitive drum, resulting in filming of talc on the photosensitive drum surface. The performance of the photosensitive drum will deteriorate.
It is therefore an objective of the present invention to overcome the above-described problems and to provide an improved image forming apparatus that is capable of properly preventing paper dust from being collected together with the residual toner, thereby performing high quality image forming operation.
In order to attain the above and other objects, the present invention provides an image forming apparatus, comprising: a paper conveying unit conveying a sheet of paper along a predetermined paper transport path in a paper conveying direction toward a predetermined transfer position; an image transfer unit located on the transfer position, the image transfer unit transferring a visible image, which is formed by development agent, onto the sheet of paper transferred to the transfer position; a first paper dust removing member that is positioned at a first predetermined position upstream from the transfer position in the paper conveying direction along the paper transport path, the first paper dust removing member removing a first component in paper dust from the sheet of paper; and a second paper dust removing member that is positioned at a second predetermined position upstream from the transfer position in the paper conveying direction along the paper transport path, the second paper dust removing member removing a second component in paper dust from the sheet of paper.
The second paper dust removing member may remove also the first component from the sheet of paper, the second paper dust removing member having a greater ability of removing the second component than the first paper dust removing member.
The image transfer unit may include an image bearing body having an image bearing surface, the image bearing surface bearing thereon the visible image that is formed through development of an electrostatic latent image by the developing agent, the image bearing surface moving along a predetermined image moving path in a predetermined image moving direction, thereby carrying the visible image, the predetermined image moving path and the predetermined paper transport path being arranged so that the sheet of paper is brought into contact with the image bearing surface when the sheet of paper reaches the predetermined transfer position, the visible image being transferred from the image bearing surface to the sheet of paper when the sheet of paper reaches the predetermined transfer position. The image forming apparatus may further comprise a developing unit developing, with the developing agent, the electrostatic latent image into the visible image, the developing unit being located at a position downstream from the transfer position along the image moving path in the image moving direction.
The first component may include fiber material of the paper dust, and the second component may include filler material of the paper dust.
According to another aspect, the present invention provides an image forming apparatus, comprising: a paper conveying unit conveying a sheet of paper along a predetermined paper transport path in a paper conveying direction toward a predetermined transfer position; an image transfer unit located on the transfer position, the image transfer unit transferring a visible image, which is formed by development agent, onto the sheet of paper transferred to the transfer position; a first paper dust removing member that is positioned at a first predetermined position upstream from the transfer position in the paper conveying direction along the paper transport path, the first paper dust removing member removing a first component in paper dust from the sheet of paper; and a second paper dust removing member that is positioned at a second predetermined position upstream from the transfer position in the paper conveying direction along the paper transport path, the second paper dust removing member removing the first component and a second component in the paper dust from the sheet of paper, the second paper dust removing member having a greater ability of removing the second component than the first paper dust removing member.
According to another aspect, the present invention provides an image forming apparatus, comprising: a paper conveying unit conveying a sheet of paper along a predetermined paper transport path in a paper conveying direction toward a predetermined transfer position; an image bearing body having an image bearing surface, the image bearing surface bearing thereon a visible image that is formed through development of an electrostatic latent image by developing agent, the image bearing surface moving along a predetermined image moving path in a predetermined image moving direction, thereby carrying the visible image, the predetermined image moving path and the predetermined paper transport path being arranged so that the sheet of paper is brought into contact with the image bearing surface when the sheet of paper reaches the predetermined transfer position, the visible image being transferred from the image bearing surface to the sheet of paper when the sheet of paper reaches the predetermined transfer position; a first paper dust removing member that is positioned at a first predetermined position downstream from the predetermined transfer position in the image moving direction along the image moving path, the first paper dust removing member contacting the surface of the image bearing body to remove a first component in paper dust that clings to the surface of the image bearing body; and a second paper dust removing member that is positioned at a second predetermined position upstream from the transfer position in the paper conveying direction along the paper transport path, the second paper dust removing member removing a second component in paper dust from the sheet of paper.
According to still another aspect, the present invention provides an image forming apparatus, comprising: a paper conveying unit conveying a sheet of paper along a predetermined paper transport path in a paper conveying direction toward a predetermined transfer position; an image bearing body having an image bearing surface, the image bearing surface bearing thereon a visible image that is formed through development of an electrostatic latent image by developing agent, the image bearing surface moving along a predetermined image moving path in a predetermined image moving direction, thereby carrying the visible image, the predetermined image moving path and the predetermined paper transport path being arranged so that the sheet of paper is brought into contact with the image bearing surface when the sheet of paper reaches the predetermined transfer position, the visible image being transferred from the image bearing surface to the sheet of paper when the sheet of paper reaches the predetermined transfer position; and at least two paper dust removing members for removing at least two components of paper dust, respectively, at least one of the at least two paper dust removing members being positioned at a position upstream from the transfer position in the paper conveying direction along the paper transport path to remove a corresponding component in paper dust from the sheet of paper that is being conveyed at the position, thereby preventing the corresponding component of paper dust from being transferred to the image bearing body at the transfer position.